Joint

ABSTRACT

A joint between two hollow pipes is formed by inserting the pipes into a sleeve. The sleeve is made of a similar or compatible material to that of the pipes which are to be joined. The inner diameter of the sleeve increases from a middle portion outwardly to two end portions. The sleeve includes a pair of tapered collars which engage each end portion and abut the middle portion. Relative rotation of the pipes and sleeve causes melting and mixing of the pipe and sleeve surfaces. This mixing action eliminates the weld line present in known systems.

The invention relates to a method and apparatus for joining together twoor more lengths of a continuous section such as a pipe or a shaft or arod, each having a substantially circular cross-section and particularlybut not exclusively to a method or apparatus for joining sections formedfrom a material which softens or melts on heating such asthermoplastics, and metals such as steel or copper.

The invention is applicable to both solid and hollow sections and isparticularly applicable to extruded plastics hollow pipe sections.

It is known to join two pipe sections by means of a friction weldingprocess. Friction welding relies on generating heat at an interfacebetween components to be welded by causing relative motion between themand applying suitable pressure on the interface to sustain the frictionforce. This motion could be linear or rotary and also could beoscillatory or continuous.

Conventionally, one of the components to be joined is moved towards orvibrated against the other. The heat generated at an appropriate rate byfriction causes a layer of the surfaces of each component to melt at theinterface. A degree of mixing of these layers due to the continuation ofrelative motion exists and the interface is gradually diffused forming acontinuation of the material across the original interface.

The motion is then stopped and cooling is allowed to occur. Theinterfacial melt layer solidifies and forms a solid joint.

A disadvantage of this known process is that it is severely hampered incases where one or both of the members of the joint is too large, heavyor already fixed in a structure, which makes the process of rotation andcreating relative frictional motion too difficult or impossible.

In addition, in the case of axi-symmetric parts, such as solid roundshafts, tubes or pipes, the welding process is restricted to formingjoints having a coaxial configuration.

In a case where the material has a molecular or crystalline structurewhich can be controlled during the manufacturing stage of a pipe or ashaft by means of rotating dies, for example, an additional disadvantageof known welding operations which rely on heat by friction or any othermeans is observed. In some cases the structure of the material is givena particular pattern of orientation which is frozen in the material.This pattern may be lost, decreased or distorted during welding byconventional means.

It is known to join two hollow pipes formed by extrusion or any othermethod by means of a hot plate welding operation. In this method theends of the pipes to be welded are placed in contact with a metal plate,which is electrically heated, one pipe at each side. The contact issustained by applying a suitable axial force to the pipes against theplate sides. After a relatively short while (a few seconds), the heatfrom the plate causes a certain amount of the pipe material to melt. Theplate is then removed and the pipes are pushed against each other.Contact takes place at the interface which is wetted by melt andsuitable axial pressure is applied. The two molten layers at each of thepipe ends achieve contact and a bond takes place. Some of the meltmaterial is squeezed out radially forming what is known as a weldingbead. Upon cooling the joint becomes permanent and the bead is removedlater by mechanical means.

Another known process for welding pipes together is a process known aselectro-fusion. In this process the ends of the pipes are inserted intoa specially designed cylindrical sleeve of suitable internal diameter.The sleeve contains a coil of electrically resistant wire incorporatedin its body near the internal surface and with electrical contacts whichare connected to an external source of electric current. With the pipesin position, the wire coil heats up upon passing a suitable currentthrough it for a given length of time. This heat melts a sufficientamount of material from the pipes and the internal surface of the sleevewhich fuse together forming a joint upon cooling. The sleeve remains inposition and becomes a part of the joint. This process requires scrapingthe pipes on site in order to expose an un-contaminated or oxidisedfresh surface.

The choice between these known methods depends on the size of pipe, thehot plate welding being used mainly in larger sizes, electro-fusion forsmaller sizes mainly due to the high cost of making a large size sleeve.In both cases there is no mixing between the melt layers as there islittle or no relative motion at the interface, therefore in the hotplate welding a weld line perpendicular to the axis of the pipes existsbetween the pipes, and in the electro-fusion welding also a weld line(or surface) exists on the interfacial circumferences between the pipesand the sleeve.

This weld line is in general a possible source of weakness, particularlyin the case of fibre filled plastics as the fibres will not cross thisweld line and thus the weld area will have different and inferiormechanical properties than the rest of the pipe.

In both cases any molecular orientation in the pipe material may besubstantially damaged or lost in and near the weld zone due to theheating and melting period. Subsequent cooling leaves the molecules inthis region in their natural pre-orientation coiled state and starved ofreinforcing fibres if present in the pipe material. Any improvement dueto the molecular or fibre orientation is thus locally lost.

These problems can be accounted for in the design, application andmaintenance procedures, which normally lead to a high factor of safetyand therefore increased material or other cost.

According to a first aspect of the invention there is provided a sleevemeans for use in joining first and second lengths of a continuoussection, each of which has a substantially circular cross-section, thesleeve means comprising:

a middle portion having an inner diameter which is substantially smallerthan the outer diameter of the sections, and two end portions eachhaving an inner diameter which is larger than that of the middleportion.

Advantageously, the sleeve means is formed from a material which iscompatible with the material of each of the first and second sections.

If the sections are formed from a similar material to one another, thenthe sleeve means may be formed from that material. However, if thematerials of the two sections are different and incompatible, the sleevemeans may be made of a third material which is compatible with each ofthe materials forming the first and second sections. This allows twoincompatible components to be joined together.

If the sections to be joined are hollow the inner diameter of the middleportion will be substantially the same as the inner diameter of each ofthe sections.

Advantageously, the sleeve means comprises a first collar and a secondcollar, and an intermediate sleeve positioned between the first collarand the second collar.

Preferably, the internal diameter of each end portion of the sleevemeans is tapered such that it increases towards the end of the sleeve.This enhances the flow of material during the melting process andensures continuous contact with the collar.

The addition of the collars on either side of the sleeve enable welds tobe carried out at any angle between the axes of the two sections to bejoined, and also allows the materials of the collar and sleeve portionto be varied as appropriate, in order that two pipes made ofincompatible materials or different grades may be joined together insuch a way as to enhance the quality of the weld.

Preferably, the sleeve further comprises an abutment portion between themiddle portion and each end portion for accurately positioning eachsection within the sleeve. The abutment portion also acts as a stop forthe collar.

According to a second aspect of the invention there is provided a methodof joining first and second lengths of a continuous section, each ofwhich has a substantially circular cross-section, the method comprisingthe steps of:

inserting each section into opposite ends of a sleeve means, whichsleeve means comprises a middle portion having an inner diameter whichis smaller than the outer diameter of the sections and two end portionshaving an inner diameter which is larger than that of the middleportion; and

rotating the sleeve relative to the sections

The method according to the second aspect of the invention may be usedin connection with sections made from any thermoplastic material,whether that material is oriented or not, and whether the material hasfibres in it or not. It may also be used in connection with the sectionsformed from metals, and any other material which may melt or soften byheat.

The method may be used in connection with solid sections, but isparticularly appropriate for hollow sections, for example, hollow pipesections.

Advantageously, the method comprises the step of rotating the sleevemeans whilst preventing rotation of the sections.

In other words, relative motion of the sleeve means and the sections isachieved by moving the sleeve means whilst keeping the sectionstationary. This obviates the need to rotate the sections themselves andtherefore reduces or completely eliminates problems associated with therotation of large masses. It also overcomes the problems which arisewhen a pipe section is immoveable, for example, because it is in a fixedposition.

Preferably, the sleeve means comprises:

a first collar and a second collar and an intermediate sleeve positionedbetween the first collar and the second collar.

According to a third aspect of the invention there is provided anapparatus for joining first and second lengths of continuous section,each of which has a substantially circular cross-section, by insertingthe first and second lengths into a sleeve system, the apparatuscomprising:

clamping means for clamping the sleeve system;

gripping means for gripping the sections; and

rotating means for rotating the sleeve system whilst maintaining thesections stationary.

The invention will now be further described by way of example only withreference to the accompanying drawings in which:

FIG. 1 a schematic representation of a sleeve according to the presentinvention;

FIGS. 2 to 4 are schematic representations of different embodiments ofthe sleeve of FIG. 1;

FIGS. 5 and 6 are schematic representations of sleeves according to thepresent invention incorporating gears on their external surfaces;

FIGS. 7a and 7b are schematic representations of a collar according tothe present invention;

FIGS. 8a to 8i are schematic representations of further embodiments ofcollars according to the present invention;

FIGS. 9a and 9b are schematic representations of another embodiment ofthe sleeve and collar system according to the present invention;

FIG. 10 is a schematic representation of a collar, sleeve and pipeassembly prior to the welding process having been carried out;

FIGS. 11 to 16 are schematic representations of collar, sleeve and pipearrangements showing possible welding configurations; and

FIG. 17 is a schematic representation of an apparatus according to thepresent invention.

Referring to FIG. 1, the sleeve according to the present invention isdesignated generally by the reference numeral 100. Two continuoussections to be joined in this case hollow pipes 1 and 2, are insertedinto opposite ends of the sleeve and held stationary while the sleeve100 is rotated. Axial pressure is applied in the direction of thearrows. Melt due to friction begins to form at circumference point C.The pipe could be chamfered as indicated by a dotted line c--c toincrease the initial contact area.

The sleeve 100 is made of a similar or compatible material to that ofthe pipes 1, 2 which are to be joined. The sleeve is generallycylindrical, with a middle disc portion 4 of internal diameter D1substantially equal to that of the internal diameter of each pipe 1, 2.In addition, the sleeve 100 has an outer diameter D3. The remainder ofthe sleeve is formed from two end portions 5, 6 which are taperedinternally. Their internal diameters increase from D3 where the middlesection ends to D4 at each end. The diameter D3 is slightly smaller thanthe external diameter D2 of the pipes 1, 2 and the diameter D4 isslightly larger than the pipe outer diameter D2.

The outer diameter D9 of the sleeve 1 is chosen to be larger thandiameter D2. The change in diameter from D2 to D4 defines an angle αbetween the internal surface of the sleeve and the outer surface of thepipe, which in turn defines two conical spaces A and B.

When the pipes 1, 2 are inserted into the two end portions 5, 6 of thesleeve 100 they contact the sleeve initially at C, or if the surface ischamfered along A, at line c--c. The axial pressure ensures this contactremains whilst the sleeve 100 is rotated. The pipes are held in positionwhile the sleeve is gripped by rotational equipment. The friction underforce at C (or c--c) causes melting to occur and the axial pressurecauses the melt to flow outwards and inwards in the conical gaps A andB, between the sleeve 100 and the pipes 1, 2 and ensures that thefrictional contact is renewed.

The rotation and axial motion under axial pressure continues until theend surface 7, 8 of the pipes 1, 2 respectively meet the end surface 9,10 of the inner disc portion 4. The melt flows to fill the gaps in A andB.

During the rotation a tangential shear stress exists between thesurfaces of the sleeve 100 and the pipes 1, 2 which causes the moltenlayers for these surfaces to form a uniform mixture. This mixing actioneliminates the weld line present in known systems as describedpreviously in this specification.

In addition the melt layer is subjected to circumferential rotation andacquires molecular orientation in that direction. This orientation islargely retained in the joint after cooling. This enhances the strengthof the joint in this region. If the pipes are orientedcircumferentially, or have a component of circumferential orientation aswell as axial orientation, which can be achieved by using a die with arotating mandrel, for example, the direction of rotation of the sleevein the welding process (ie clockwise or anti-clockwise) can be chosensuch that the welding melt has circumferential molecular orientation inthe same direction as that of the pipes 1, 2.

For fibre filled pipes, similar material is used for the sleeve withsimilar fibre concentration. The mixing action of the shear duringrotation and melting will cause the fibre to cross the boundary betweenthe pipe material and sleeve, and also acquire a similar orientation inthe same way as that described above, and thus avoid the formation of afibre starved weld zone.

FIGS. 2 to 4 illustrate further possible shapes for the sleeve accordingto the present invention.

FIG. 2 illustrates a sleeve 200, which has straight edges and can beused to produce a joint for the same internal and external diameters asthe pipes 1, 2. FIG. 3 illustrates a sleeve 300 having the same elementas those shown in FIG. 1, but allowing an increased area for frictionalmelting and works like sleeve 200. FIG. 4 illustrates a similar sleeve400. Pipes 1, 2 to be joined using a sleeve 400 (FIG. 4) have to havetheir ends chamfered or machined as shown, to ensure good initialcontact with the sleeve.

Referring to FIGS. 5a, 5b, 6a and 6b, a sleeve 500 is illustratedschematically. The sleeve 500 comprises grooves in the form of gearsformed on an outer middle portion 510 of the sleeve 500. The gears orteeth are included to be engaged with rotational equipment in order tofacilitate rotation of the sleeve. The teeth can be moulded into thesleeve or they can be machined afterwards.

The sleeves illustrated may be moulded with internal metallic insert toenhance the rigidity and strength of the sleeve especially in the caseof soft materials.

For use with the pipes which are not coaxial or of different sizes, thesleeve is manufactured with two or more cylindrical openings, the centrelines of which are aligned along any desired direction relative to eachother.

Referring to FIGS. 7a and 7b, a sleeve system according to the presentinvention is designated generally by the reference numeral 700. Thesleeve system 700 comprises two collars 710 (only one of which isshown), positioned on either side of a sleeve 720. The collar may alsobe made by moulding or machining from a material similar to orcompatible with that of the pipes. During welding, the pipes (not shownhere) and sleeves 720 are held in position whilst the collars arerotated simultaneously, or one at a time depending on the type ofequipment used.

The sleeve 720 comprises a two step internal diameter of the middlesection. The first internal diameter is used to locate a pipe 1, and theinternal second diameter is used to mark the end of the axial travel ofthe collar when it is being appropriately positioned.

The collars 710 each have an internal diameter D5 equal to the outerdiameter D2 of the pipes 1, 2. The internal surface of each collar 710continues at this diameter for a distance S, and then increasesgradually to D6 which is larger than the outer diameter D2 of thepipe 1. The external surface of each collar has a diameter D7, which islarger than D3. It increases gradually towards the opening to a diameterD8 which is smaller than D4. The collar comprises a flange 730 at anouter end having a diameter D6.

When each collar 710 is rotated, the process is exactly as describedearlier and welding occurs at the inner and outer surfaces of thecollar. Each collar may also be fibre filled, reinforced with an insertand its flange may be formed as a gear to enhance the gripping androtation action of the rotational equipment used to rotate the collar.The gear teeth or serrations or grooves can either be on the externalsurface of the flange, or on the internal surface near the edge.

Melting occurs on the surface S and C and the melt flows under axialforce in the direction of the pressure P into gaps A, B, C. The welding,melt formation and orientation of molecules and the fibres takes placein the same fashion as explained above.

FIGS. 8a to 8f illustrate different designs for collars and FIG. 8g to8i illustrates an example of a sleeve. The internal grooves in FIG. 8calso act as melt channels. FIG. 10 illustrates an assembly of thesimilar pipes 1, 2, collars 710, 720 and sleeve 730 positioned prior tothe welding operation.

The sleeve 710 can have two different sizes and positions for weldingpipes with different dimensions.

FIGS. 11 to 16 illustrate different designs of pipe, collar and sleeveassemblies showing the different angles which may be achieved by meansof the present invention.

Referring to FIG. 17, an apparatus for forming a welding joint accordingto the present invention is illustrated generally by the referencenumeral 1700. The apparatus 1700 is used to grip a sleeve assemblyaccording to the present invention, and to rotate collars in anarrangement similar to FIG. 11. It can also be used to grip pipes androtate the sleeves for cases where the pipes are coaxial, and directrotation of the sleeve achieves the welding without using a collar asdescribed with reference to FIG. 1.

One unit can be used to create one joint at a time at each end of thesleeve, or in the case of multiple joints such as those illustrated inFIGS. 11 to 16, at each opening. Alternatively, more than one unit canbe combined to perform more than one joining operation at the same timeat each end or opening of the sleeve.

The apparatus 1700 comprises a frame made up of two parallel brackets Aand B made of steel plates and shaped with a semi-circular opening inthe middle, to allow for the pipes and sleeve to be placed within thebrackets. The brackets are fixed to a base E a suitable distance apart.Each of the brackets A and B carry a clamping mechanism C and Dcorrespondingly. Clamp C holds the right hand side pipe in a fixedposition, and clamp D holds the sleeve in a fixed position.

The clamping action is achieved by means of toggle mechanisms T,T₂ whichoperate clamping pads C1, C2 and D1, D2 by means of handles P1 and P2.The action of the handle P1 are transmitted to C1, C2 and D1, D2 bymeans of a series of levers C3 to C8 as shown. Similarly the action ofhandle P2 is transmitted to D1, D2 by an identical mechanism comprisinga set of levers D3 to D8 also identical to C3 to C8.

The pads C1, C2 and D1, D2 have the same radius as the pipe and thesleeve respectively and the same centre O1 and thus ensure that thesleeve and the pipe remain concentric throughout the operation.

The bracket A carries two round polished linear motion guides H1 and H2fixed to it at one end by means of screws S1. The guides H1, H2 extendhorizontally through a floating bracket F, placed between A and Bthrough guide holes R1 within F and further through B through guideholes R2.

The guides H can be fixed at R2 by means of screw S2. This allows theinitial distance between A and B to be adjustable as required beforefixing them to the base E.

The dimension of holes R1 are such that the floating bracket F can slidealong H.

The floating bracket F has a similar semi-circular opening as that ofbrackets A and B. It also has two wheels W1, W2 fixed to rotate freelyon two shafts mounted on F and can move towards or away from the centreline of the assembly by means of a screws S3, S4.

The wheels W can be brought into contact with the collar 2 by moving Faxially.

The floating bracket is connected on both sides of the pipe to the fixedbracket A by means of a symmetrical system of levers F1 and F2 which arepivoted to it and also to levers G1 and G2.

The levers G1 and G2 are fixed to a connecting rod Q which penetratesbrackets A and is pivoted about the centre line X1-X2.

The lever P3 can thus operate G1, and also G2 via Q to move the floatingplate axially.

The bracket F extends vertically behind the assembly where anotherbracket J is hinged to it about centre O2.

A lever K is attached to J and is used to turn J about O2 to adjust itsangular position. A motor U attached to a gear L which is mounted on Jsuch that its axis O3 is parallel to the axis of the pipe 01. The lengthO2-O3 is chosen such that when J is lowered by means of K, the gear Lcomes into contact and engages with the integral teeth on the flange ofthe collar.

The gear L can be replaced by another means of transmitting rotarymotion to the collar or the sleeve for the case when there are no teethintegral with the flange. Such means could be a rubber wheel, instead ofthe gear, which drives the flange by frictional contact without slip.

Method of Operation

1. The sleeve 1 is fixed in position by means of the pads D1, D2 and theaction of lever P2.

2. The collar 2 is slid on the pipe 3 prior to clamping the pipe in itsfixed axial position, and then the collar and pipe are moved axiallytowards the sleeve until the pipe resets within the central portionprovided for it as described above.

3. The pipe is then clamped by means of C1, C2 and the action of leverP1 as described above.

4. The collar is then slid on the pipe axially towards the sleeve untilit contacts the tapered internal end portion of the sleeve 100.

5. The lever K is then used to lower J such that L engages the collar.

6. The lever P3 is then used to slide the floating bracket F towards thecollar and contact is achieved between the collar and the wheels W.

7. The collar is thus axially constrained by the contact with the sleeveand the wheels W. The motor is then switched on and the collar begins torotate at the required speed, typically about 500 R.P.M. The motion ofP3 is continued until the flange edge contacts the edge of the sleeve oruntil it is stopped by other means at a position adjusted prior to theoperation.

Mechanical or electrical means can be placed on the guides H to assistthe axial location of the sleeve and end the sliding of bracket F.

The rotation is maintained for a few seconds, when the final axialpositioned has been reached.

The process of melting by frictional heat, melt rotation viscous heatingand orientation take place as described earlier followed by cooling,solidification and formation of the permanent joint as describedearlier.

I claim:
 1. A sleeve means for use in joining, by melting, first andsecond lengths of a continuous section, each of which has asubstantially circular cross-section, the sleeve means comprising:amiddle portion having an inner diameter and two end portions each havingan inner diameter which is larger than that of the middle portion; afirst collar removably engageable in a first end portion, and abuttablewith the middle portion, and a second collar removably engageable with asecond end portion and abuttable with the middle portion, the middleportion forming an intermediate sleeve portion, and the first and secondcollars each adapted to receive a length of continuous section;characterized in that the internal diameter of each collar is taperedsuch that it increases towards one end of the collar, and in that theouter diameter of each of the collars tapers towards the other end ofthe collar at a substantially different angle to the angle at which theinner diameter of the respective end portion of the sleeve tapers, suchthat the outer tapered diameter of the collar and the inner diameter ofthe end portion are spaced apart from one another, whereby relativerotation of the continuous sections and the sleeve means results inmelting of the continuous sections and the sleeve means, thereby forminga weld.
 2. A sleeve means according to claim 1 wherein the sleeve meansis formed from a material which is compatible with a material of each ofthe first and second sections.
 3. A sleeve means according to claim 2wherein the intermediate sleeve further comprises an abutment portionbetween the middle portion and each end portion.
 4. A sleeve meansaccording to claim 1 wherein the intermediate sleeve further comprisesan abutment portion between the middle portion and each end portion. 5.A method of joining first and second lengths of a continuous section,each of which lengths has a substantially circular cross-section, themethod comprising the steps of:inserting each section into opposite endsof a sleeve means, which sleeve means comprises a middle portion havingan inner diameter and two end portions having an inner diameter which islarger than that of the middle portion and a first collar removablyengageable in a first end portion, and abuttable with the middle portionand a second collar removably engageable with a second end portion andabuttable with the middle portion, the middle portion forming anintermediate sleeve portion, and the first and second collars eachadapted to receive a length of continuous section wherein the internaldiameter of each collar is tapered such that it increases towards theends of the collar, and in that the outer diameter of each collar taperstowards the end of the collar at a substantially different angle to theangle at which the inner diameter of the middle portion tapers such thatthe outer diameter of the collar and the inner diameter of the middleportion are spaced apart from one another to facilitate flow of meltedmaterial and continuous contact with the collar; and rotating the sleevemeans which preventing rotation of the sections which rotation causesmelting, due to friction of the sleeve means and the continuoussections, thereby forming a weld.
 6. Apparatus for joining first andsecond lengths of continuous section, each of which lengths has asubstantially circular cross section which lengths are to be joined byinserting the first and second lengths into a sleeve means the sleevemeans comprising a middle portion having an inner diameter which issubstantially smaller than the outer diameter of the sections, and twoend portions each having an inner diameter which is larger than that ofthe middle portion; a first collar removably engageable in a first endportion, and abuttable with the middle portion, and a second collarremovably engageable with a second end portion and abuttable with themiddle portion, the middle portion forming an intermediate sleeveportion, and the first and second collars each adapted to receive alength of continuous section; the apparatus comprising:clamping meansfor clamping the sleeve system; gripping means for gripping thesections; and rotating means for rotating the sleeve means whichmaintaining the sections stationary.